Response on web should looks similar to this one (btw: one below is of course for different payload):

---<response>---
</head>

<body>
<h1>Internal Server Error</h1>
<h2>CDbCommand failed to execute the SQL statement: SQLSTATE[42000]: Syntax error or access violation: 1064 You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near &#039;&quot;%&#039;;/**;--# = &#039;a&#039;)&#039; at line 4</h2>
<p>
An internal error occurred while the Web server was processing your request.
Please contact the webmaster to report this problem.
</p>
<p>
Thank you.
</p>
<div class="version">
2015-11-04 08:29:59 </div>---</response>---